Our specific objectives are the following: 1) To further define the molecular nature of the (Ca -Mg -ATPase energizing Ca ions transport by sarcoplasmic reticulum with particular emphasis on the role played by the membrane lipids in this activity; 2) To analyze the molecular basis of Ca ions binding by sarcotubular membranes, in particular the mechanism by which ATP-dependent binding occurs and the role lipids play in it; 3) To attempt to reconstitute the sarcotubular membrane system at least in terms of its Ca ions transport function from the isolated lipid components of these membranes and the Fraction 2 protein, the lipid-poor, water-soluble major protein component. For these studies, the highly purified sarcotubular membrane fraction we call SF1 will be utilized. The lipids and the well-characterized protein components of SF1 will be isolated. Experiments involving the measurements of ATP-independent Ca ions binding, ATP-dependent Ca ions binding, (Ca -Mg - ATPase activity, Ca ions transport will be carried out with intact sarcotubular membranes, perturbated sarcotubular membranes, isolated membrane components and lipid-protein complexes prepared from isolated membrane components. Although the sequestration and release of Ca ions by sarcoplasmic reticulum plays a central role in muscle physiology it is still not clear whether Ca ions transport or Ca ions binding by sarcotubular membranes or both is or are involved. This research will yield significant information in this regard and in regard to the pathophysiology of cardiac and skeletal muscle diseases and the mechanism of action of therapeutic agents used in these diseases. Moreover this work should provide significant data on the molecular nature of this membrane relative to its function and thus provide information basic to the general field of membrane biology. Since many of the diseases, for which either understanding or adequate therapy is currently lacking, may well relate to membrane dysfunction, this research should yield information basic to the development of medicine in these areas, e.g., diabetes mellitus, multiple sclerosis, immune diseases, etc.